Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: adriangsmith on April 13, 2018, 08:15:25 PM
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Hi All,
I can't get a spark out of my newly built 400/4.
have fitted new points and condensers, set gaps and timing.
Get spark at the points but not from the plugs.
Have checked 12v at black white wire on coils, earthing from coils to frame and continuity of the blue and yellow wires to the points. checked and changed plug caps to no effect. Have also checked engine kill circuit and neutral switch. Starter motor works OK.
Coils are getting warm so assume they are getting power.
Apart from this i do not know how to check the coils themselves.
What am I missing??
TIA
Adrian
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Sounds like you have assembled the wiring to the points wrongly. The wire that attaches to each set of points should have insulating washers either side of the terminal on the wire. The terminal MUST NOT be in contact with the body of the points, ONLY the spring, otherwise you have the coils permanently grounded and they wont spark!. Also, did you clean the faces of the points? They are coated with an anti corrosion grease/gunge which must be cleaned off.
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Assuming the 12v on the coils is ok (black/white), unplug the blue and yellow wires by the brake switch. If you momentarily earth the negative end of the coil, you should get a spark. I'm thinking the same as Hairy: you've got a permanent ground on the points, which is why the coils are getting hot.
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To check the coils you need to disconnect them then take a primary and a secondary reading with an ohm meter I don't know the exact figures but the primary which is taken between the 2 thin leads should be about 4-7 ohms and the secondary taken between the 2 ht leads should be somewhere between about 25000 to 35000 ohms if you check both of them they should be roughly the same , usulay if the coil is knackered you will have an open circuit between one of them.
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To check the coils you need to disconnect them then take a primary and a secondary reading with an ohm meter I don't know the exact figures but the primary which is taken between the 2 thin leads should be about 4-7 ohms and the secondary taken between the 2 ht leads should be somewhere between about 25000 to 35000 ohms if you check both of them they should be roughly the same , usulay if the coil is knackered you will have an open circuit between one of them.
Hi all.
Problem solved. Forgot to clean the points contacts!
Always the simple things that get missed!
Fired up first time.
Sent from my LG-H870 using Tapatalk
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You'd be amazed how often it happens, you are not the first, and certainly wont be the last! As I said, the grease/gunk they put on at the manufacturing stage stops corrosion in storage/transit, but nowhere does it tell on the packaging (or in most manuals!) that it needs to be wiped off before using. Glad it was something so simple and it's up and running now. ;D
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Always good when you find it and it's an easy fix that's part of the fun nice one.
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Hi all,
this is probably the most relevant thread for my issue! Funny but I had exactly the same issue and solved by cleaning the points - felt like a numpty but it's always the simple things - well said!
So... (1976 cb400f) I checked my spark plugs and I've got two NGK DR8ES-L - which I've recently found out are not what I need, but are the one's I got sent by davidsilverspares (the original NGK D8ES-L are not easily available anymore). I've also got two NGK D8EA - which I've read are the best replacements for the D8ES-L.
My problem is the threads in the engine case only accept one of the plugs, not the other. I.e. I can thread in a DR8ES-L into cylinder 3 but not 4, but I can also thread a D8EA into cylinder 4 but not 3.
Question 1 - WTF!?
Question 2 - is this normal or do I need to re-tap the case to allow the D8EA plugs to go in?
Thanks for any help or advice!
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Sounds like something not quite right there as all threads are the same on all the plugs you have mentioned 🤔D8EA should fit in all 4 ports no problem......has someone re tapped incorrectly in the past ?. Also, have you started them off with your fingers first so you can actually feel the threads catching correctly?
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Thanks for a speedy reply!
Yes, very odd! I don't know that the ports have been re-tapped in the past, but this may be the case.
I looked at the threads on the plugs and they appeared identical (by eye). But yes, it's like the ports are threaded only for the specific plug, but that's odd if the threads on the plugs are the same. :-\
I've started them all off by hand to make sure they're settled before starting with the socket-set. When in the 'wrong' port they start fine and then slow right down as if they're tapered.
I've seen some stuff online and on forums about thread 'chasers' and re-tapping etc. Just don't want to have to take the engine out if I don't need to - it's so close to running! ::)
thanks
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Same as Julie's view, something distinctly odd about that as they should all be the same.
In the past and when they where contemporary, a friend with engineering shop could leave a milling machine setup specifically for these engines so numerous did they encounter problems with plugs that hadn't been changed on centre two cylinders and seized into the head.
It's quite likely that the centre two have been worked on to correct plugs that corroded in there, quite what form you'd need to establish. It's not a show stopper but you need to evaluate to see what you've got.
Could someone have chased the two plugs down with die to get them fitted? Do they spark ok to try it without having to immediately replace those two odd plugs?
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Well that definitely makes sense if someone's had to do some work to get seized plugs out. Odd that the DR8 plugs seem to fit.
I'm pretty sure they spark but I'll have to wait till next week to double check - if they do spark is it a disastrous idea to run using different spark plugs as long as they fit?
Thanks
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They'll work ok, we talk about it on here as regarding R versus non R plugs for which there is a consideration as to their effects. I'd certainly deal with that later if you want to run it now.
You'll be able to ride and assess it ok with the mix (although though technically incorrect) they'll not cause any damage, then work out a strategy to get to where you can sort it. It's no sweat at the moment if they spark ok.
If you can work out what you need to do to get it sorted it's probably better not to get something jammed in there right now as it could snooker you for easiest fix.
Thread is 12mm times 1.25 pitch for a tap to run through the existing setup to chase out the tight ones, so could be a mid term plan to sort it. Failing that, more detailed removal of head to assess may be another course to take, sounds drastic but it's fairly routine on these to give a concise view of condition and action required.
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Brilliant! Thanks for the insight. My biggest worry was keeping them both and doing damage. I’d seen a post discussing the R and it sounded like it wasn’t a good idea but I couldn’t figure out why, but if it’s not going to stop me running it for now it’s something I can fix over the winter then that’s great!
Thank you for the help! :)